Today’s emphasis on linear actuators requires a similar emphasis placed on the actual motion which is created by the actuator. The two main ways to produce this motion rely on lead screws and ball screws, each of which has their own uses and advantages over the other. In this article, we will look closer to each type and find the difference between ball screw and lead screw.
How Do Ball Screws Work? Main Principles.
Ball screws are mechanical linear actuators which create linear motion without friction. They are used in industries where there are high thrust loads, as that is something which they can easily withstand. Their shafts are often made by rolling them out, which gives an operation precision of several thousands of an inch per foot.
Ball screw actuators feature bellows made out of either rubber or leather, a fairly bulky cylinder to allow for recirculation of the balls which are what cause the movement. They have linear seals along the seam, long carriages for the motion, and various lubrication openings at easy to access points along the mechanism.
Lead screws are links between different areas in a mechanism, and they are used to create linear motion from rotational motion. Screw threads themselves are divided into two parts, a male and a female, and the separation and linking of these two parts is something which causes a lot of friction to build up in the equipment.
Features and work principles
A lead screw actuator has a compact form, along with a rotating nut inside a cylinder. The motor in linear screw drives is constrained within the cylinder – it is the nut which moves. These electric screw actuators are self-locking, and have a minimum number of moving parts. Finally, they sometimes have half nuts installed which can disengage the nut if needed.
One of the popular types of the lead screw is acme screws. These screws, in particular, come with a twenty nine degrees thread angle, something which is easier to create than a square thread. While the increased friction of a triangular thread makes it more inefficient than square ones, these threads are also much stronger, and are therefore the acme screw linear actuators are able to provide more load-bearing capabilities.
Advantages of Ball Screws
- Ball screws are much more efficient, since they sacrifice a lot of torque through their construction – they are more flexible;
- They have lower friction due to the way they are created, and this means that they do not heat up in the same way as a lead screw linear actuator would in a similar situation;
- The construction means that they are less liable to break down and need maintenance.
Ball Screw Disadvantages
- Ball screws are not capable of self-regulation – the linear screw actuators they are incorporated into thus requiring separate brakes put on them. These braking mechanisms are specifically required to prevent back driving, which would be bad for the screws;
- Vertical applications and equipment can be difficult for ball screw actuators;
- These types of screw are incredibly noisy, which does limit their applications and uses;
- They are very bulky, which limits them to applications which have lots of available space;
- A screw driven linear actuator which uses ball screws will need more and more regular lubrication than other types of screw;
- Also, they cost more than lead screws do.
Advantages of Lead Screw
- They are cheaper;
- Lead screws, and the acme screw actuators which they are in self-lock – they do not require a separate braking system to be installed.
- They are more efficient when it comes to vertical applications and equipment.
Lead Screw Disadvantages
- Lead screws need to be replaced much more frequently than other screws;
- They are inefficient, due to the way they are constructed. The need for a larger motor, and the existence of torque due to the screws lack of flexibility, makes them less efficient to use and work with;
- The construction means that they produce more friction when working, and so produce more heat;
- They are not capable of handling high throughout, higher speeds, or longer cycle times.
This article was to discuss the differences and similarities of lead screws and ball screws, and whether one or the other was better. We ourselves use lead screws in acme thread actuators, but ball screws have their place in many applications and processes. Lead screws are less expensive than ball screws, but the issue of which type of screw to use is one which is much more complicated than simply the issue of cost – each one has advantages to particular uses, which means that sometimes it is contingent on the user to look beyond cost to what would be most appropriate.